1. Field of the Invention
This invention pertains to transistor saturable reactor circuits sometimes referred to as multivibrators and in more recent electronic terminology as inverters or D.C. to D.C. converters. Hereinafter, they will be termed multivibrators. More specifically this invention pertains to a circuit method of preventing transistor failure due to a loss of transistor switching action when a load short circuit occurs. Switching action is continued by feedback energy supplied from a separate base drive transformer by way of windings in the emitter circuits of the two transistors.
2. Description of the Prior Art
It is common knowledge that when the load of these devices, prior to my invention, suffers a short circuit, switching action ceases because the feedback signal is no longer available at the output transformer. Invariably one transistor hangs up and stays on while the other remains off. The "on" transistor burns up because it is then subjected to a one hundred percent duty cycle with almost twice the power dissipation that it would have if it were switching. Attempts have been made to devise circuits that will prevent this catastrophe but none of them have proven satisfactory to date.
Multivibrators with feedback taken from collector windings as well as those with feedback from emitter windings have long been known. This circuit provides a means of combining a collector feedback multivibrator with one having feedback supplied by emitter current. By the use of an ingenious electronic barrier between the two commonly known sources of feedback the circuit can be made to oscillate in either of the two modes depending upon whether the collector feedback voltage is strong enough to overcome the barrier. The circuit is simple and rugged, requiring a minimum of parts and giving very reliable operation.